SILICATES. 287 



heat it over a lamp fed by bellows. The water from 

 talcose minerals is only driven off at a white heat. 



This temperature may be obtained by using the 

 lamp represented in Fig. 43. The apparatus is com- 

 posed of three principal pieces: a bottle A communi- 

 cating with the tube E with the reservoir I of spirits 

 of turpentine or the lamp proper, which communi- 

 cates by the double tube G with an apparatus for the 

 distribution of air forced by the bellows K, which 

 feeds at the same time the tube H.* 



Generally when minerals lose their volatile matter, 

 only at the temperature attained by the large lamp, it 

 is those containing fluorine, and it is then necessary 

 first to examine the nature of the volatile matter. 



The calcination is carried on until neither water nor 

 fluorine remains. 



It should be noticed whether any material is lost in 



* Fig. 46 shows the interior construction of the lamp. The 

 annular space is closed on all parts, above and at the side by 



Fig. 46. 



a thick plate ; below by a copper plate raised externally in such 

 a manner as to form a little cup around the lamp in which water 

 is poured. 



For the management of this lamp we refer to the article by 

 M. H. Deville, Annales de Chimie et de Physique, 3d series, vol. 

 xlvi. 



